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Annoying Brake ScreechQ:I have a 2002 Ford Ranger that's had front-brake problems every 1500-2000 miles since it was brand-new. The problem starts as a rubbing noise, whether or not I'm stepping on the brake pedal. The noise is audible only at speeds of less than 25 mph and increases and decreases in frequency with the speed of the vehicle. When I first start driving, I can hear it, but by the end of my 40-mile commute, it's very noticeable in the cab. The dealer has replaced the brake pads (more than once), the rotors, and something he called the "cradle" for the pads, to eliminate vibration. It appears to make one rubbing noise per rotation of the tire; it rubs for half a rotation and doesn't rub for the other half. Would drilled brake rotors and aftermarket pads be a good move?
A:Cross-drilled brake rotors are a performance modification that provides additional heat dissipation. You get what you pay for when dealing with aftermarket pads, and original-equipment linings are often higher quality. The noise occurring with your foot off the brake pedal makes me think it's not coming from the pads themselves. If there was a frozen caliper producing a brake drag, chances are there would be more severe heat-related symptoms. The first thing to inspect is the protective shield backing the rotor. It may have become bent somewhere down the line and is now touching the rotor. The noise coming and going with rotation could be from contact with an imperfect machined surface or a rough cast portion of the rotor. This type of contact can vary with expansion and contraction of the brakes and therefore produce changes in noise levels while driving. There are other potential causes, possibly even something rubbing against the inside of a wheel. Get it to the repair shop while the noise is pronounced. They may be able to put the vehicle up on a lift, spin the wheel, and see and/or hear exactly where the sound originates.
How Much Power NowQ:I did a few performance modifications to my 2002 Dodge Ram 1500 pickup with the 5.9-liter Magnum engine. I've added the Gibson split-rear exhaust, K&N AirCharger, Tornado Fuelsaver, and a Superchips Microtuner. What horsepower numbers can I expect with these add-ons? When it was stock, the truck had 245 horses and 335 pound-feet of torque. I think I should be at or near 300 horsepower and am thinking about adding headers. Let me know where I'm at and where I need to go to compete with the Fords, Chevrolets, and the new Nissan.
A:The majority of aftermarket performance-parts manufacturers advertise an approximation of power gain with the installation of their products on your car or truck. However, accuracy can only go so far, with numerous variables between the test vehicles and your own, unknown quality and integrity of the test equipment, and the folks behind the switch. There also may be discrepancies when adding on multiple components from different companies. In other words, one company saying its component adds 10 horsepower and another boasting 15 may not add up to 25. The best way to calculate peak horsepower and torque ratings is with a dynamometer, with a qualified technician running the test. However, this brings up a communication barrier. Most automotive manufacturers publicize their power numbers in an SAE Net Rating. This is done with an engine dynamometer, taking measurements at the crankshaft with the engine out of the vehicle on a test stand. I don't know how many amateur drivers are willing to pull an engine to satisfy their curiosity. The more convenient and common method, using a chassis dynamometer, provides ratings at the driven wheels. These numbers are always lower, due to the power lost to friction between the crankshaft and tires (torque converter, transmission, driveshaft, and so on). Find a performance-oriented shop with a good reputation and realistic records of vehicles tested before and after the installation of hi-po components. This can give you a good idea as to where you stand within the Big Three--or Four.
Brake Rotor TechQ:Here's a puzzle for you: I have a 1998 Silverado Z71 with a MagnaCharger, and every 5000-6000 miles I have to turn or replace the front rotors. The dealer can't find anything wrong in the brake system. I don't drive with my foot on the brake, but they're hot after a short trip. My truck has 71K miles, and I can't afford to keep replacing the rotors. Should I go to special brakes, or is there a link in the brake system being overlooked by the dealer?
A:The add-on supercharger leads me to believe there may be some hard driving involved, and that's a major factor in the recurrence of brake pulsation. I don't see aftermarket pads helping without a loss in brake performance. With that said, keep in mind the effects of typical wheel-mounting. Many people don't realize that improper torque and/or tightening sequence can cause excessive rotor thickness variation, often making it necessary to resurface or replace the brake rotors. Every time a wheel goes back on a vehicle, the lugs need to be run down in a star pattern at the manufacturer's torque specifications. Next in line is rotor resurfacing techniques. The optimum tool is an on-car (or truck) brake lathe (GM recommends the Pro-Cut PFM900 and Hunter 0CL360). This allows rotor resurfacing that compensates for hub and hub-to-rotor mating irregularities when applicable. Along with proper tools and a quality finish, cleanliness is also important. Deposits at the hub and rotor-mating surfaces must be removed to ensure a true fit. Manufacturers even recommend marking rotors to allow reinstallation exactly the way they came off. I also pulled up a relevant Chevy Technical Service Bulletin (01-05-23-001A). It describes a kit and procedure to maintain minimal lateral runout when an on-car brake lathe isn't available. It's referred to as Brake Align and involves the installation of correction plates fitted between the hub and rotor to achieve a lateral run-out at or below the 0.050mm (0.002-inch) specification. This only applies to separate rotor/hub configuration. Take all this into consideration, and hopefully you can reduce brake-rotor expenses.
Disappearing DegreesQ:I have a 2000 Dodge Durango with a 4.7-liter engine. My question is about the outside temperature gauge. The SUV has an LED display that shows the trip computer, miles per gallon, compass, and more. Lately, the degree reading occasionally gets stuck on a reading I know is not true. For example, when I know the outside temperature is more than 95-degrees Fahrenheit, the LED reads 76. This problem is sporadic, and I don't want to spend $150 on a Dodge repair manual to find the sensor to test.
A:I don't think a service manual will be much help here. The Ambient Temperature sensor is a variable resistor mounted to a bracket behind the grille at the right-front side of the engine compartment. Testing for an inaccurate reading as opposed to a hard failure can be difficult. The sensor resistance specifications are limited to 336 kilohms at -40 degrees F and 2.488 kilohms at 131 degrees. If it measures in between, the service procedure instructs you to move on to the next step, which is a basic test looking for a short or open circuit within the sensor, which would've prompted an error message on the compass mini-trip display. Further diagnosis involves testing for excessive resistance or shorts in the sensor circuits, a self-diagnostic test of the compass mini-trip computer, and a follow-up with the appropriate scan tool. A smart shortcut would be to replace the Ambient Temperature sensor with one you know is working properly. That's probably the first place a Dodge technician would go before investing a lot of diagnostic time. The service department often has the advantage of borrowing parts for test purposes, whereas outsiders may be forced to buy parts with no refund. If a new sensor doesn't correct the problem, the repair entails a detailed hunt for poor connections or shorts and potentially having to replace a defective compass mini-trip computer.
Tired WipersQ:I have a 1996 GMC Sierra, and when I use my intermittent wipers, they sometimes stop in the middle of the windshield for a few seconds. Is this a sign that the wiper motor is starting to go, or could it be something else? My truck has 114,000 miles on it.
A:It's probably not the motor itself, but close. Start with a call to GMC at 800/462-8782. There's a recall in effect, referring to intermittent or completely inoperable wiper motors on a large group of 1994-1997 GM trucks, SUVs, and minivans (Recall #03023). Make sure you have the truck's VIN handy when you make the call. The defect involves cracked solder joints at the controller circuit board, attached to the wiper motor. If your Sierra is on the list of affected vehicles, any GMC service department should replace the circuit board at no charge, with no time or mileage limitations. If your particular pickup isn't on the list, or records show the recall repair was already completed, the problem may lie elsewhere, but the circuit board would still be high on the list of potential causes.
Ford Rearend ChatterQ:I have a 2002 Excursion with the heavy-duty tow package, 7.3-liter diesel, and limited-slip differential. At about 25,000 miles, I heard a chattering noise while accelerating into a turn. It was notably worse with a 2000-pound trailer in tow. I took it in, and the dealer replaced the differential pack. Ten thousand miles later, it started up again. I took it to another dealer, who added a friction modifier to the rearend. It worked its way in and the problem subsided after a few hundred miles. Now at 44,000 miles, it's doing it again, albeit less than before. I went back to the dealer, who was again advised by Ford tech support to add the friction modifier, but mentioned that some chatter is normal in Excursion and Super Duty rearends. I tow about 10 percent of the time and only at about 40 percent of the truck's rated capacity. What's going on here?
A:Every clutch-type limited-slip differential has the potential to chatter on turns. While driving straight ahead, it keeps the two axles locked together to improve traction. The clutches are calibrated to break free and slip at a specified torque and allow the two wheels (or two pairs on a dualie) to rotate at different speeds when making a turn. Occasionally, the lubrication property of the rear axle fluid breaks down, causing the smooth slip to become a stickier chatter. Each individual rear axle design is more or less prone to the condition, and your extra-large SUV seems to be at the top of the list. I wouldn't be all that concerned, but here are a couple of items to keep in mind. First, ask the service department to determine exactly which rear axle your Excursion has. The book shows several choices, but most Excursions use the Ford 10.5-inch rear-axle assembly with the Traction-Loc differential. This unit should use nothing but SAE 75W-140 synthetic rear-axle lubricant after the installation of Additive Friction Modifier. Another axle may require a different grade lubricant. Immediately after service, you or the technician should go to a parking lot, cut the steering wheel all the way in one direction, and do about 20 circles, then cut it the other way and do 20 more. This is the best way to work the additive into the differential's clutch material. Ford considers a slight chatter noise on slow turns after extended highway driving an acceptable characteristic with no detrimental effects. If service quiets things down, go through this process when necessary.
Cadillac Cooling WoesQ:We were thinking about buying another Cadillac Escalade, but we recently had problems with the air conditioner. The dealer installed another fan to help cool the engine. I saw the directive from Cadillac and this was the proper fix directed by the manufacturer. The fan was noisy. It sounded like a vacuum cleaner and caused the engine to run rough. We had the fan removed and are now considering a trade for something else. If you can, please let me know if the new Cadillac convertible has the same engine/air-conditioner combination?
A:That's quite a jump from the big, bouncy luxury SUV to the XLR, Cadillac's new two-seater convertible. The Caddy TSB comes right out and tells us that the auxiliary coolant fan "will create a roaring sound when operating." Hey, at least they're not trying to hide anything! The installation of the electric fan in front of the A/C condenser was an attempt to improve air-conditioning performance while idling for extended periods of time. This was to compensate for insufficient airflow produced by the mechanical clutch fan. Sounds like the additional alternator load from the fan motor may have lessened idle quality. The TSB applies to a large number of GM full-size SUVs with the 6.0-liter V-8, but it doesn't seem to be a widespread problem. I took a look at a 2004 model, and GM hasn't included the auxiliary fan in new production. To be safe, do a thorough road test of a new Escalade to ensure good duct temperature in high ambient-temperature and dense traffic conditions before taking the big step. The XLR is an all-new luxury/performance roadster to help GM keep up with the Mercedes-Benz SL500, Lexus SC 430, and Jaguar XK8 competition. You'll see the all-out sports-car version of the new platform with the unveiling of the 2005 Corvette. The XLR uses a high-output 4.6-liter V-8 pushing 320 horsepower, and chances are good that any Escalade air-conditioning shortcomings shouldn't be a factor with this extremely dissimilar vehicle.
How To Reach AlexIf you have a technical question regarding your pickup, SUV, or van, feel free to contact Alex, a master technician with the National Institute for Automotive Service Excellence. Send a letter to him in care of Truck Trend Garage, 831 S. Douglas Street, El Segundo, CA 90245, or e-mail us at trucktrend@sourceinterlink.com. Please include the VIN with your question. Due to the volume of questions received every month, we cannot guarantee that everyone's question will be personally answered or will appear in the magazine.
Can't wait for help with a problem you're having with your Truck or SUV? Ask the expert we trust here at Truck Trend Garage--visit Alex Steele at www.RealWorldAutomotive.com.
